Acrylate polymer is a highly transparent polymer and is suitable for use as a material for making long distance optical telecommunication products. However, C—H bonds of the acrylate polymer will absorb signals having a wavelength of 1.2-1.6 μm used in the telecommunication, which results in an optical loss. Halogen-containing acrylates having a less number of C—H bond have been developed and used, as a replacement of the acrylate polymer, for making improved optical telecommunication products in terms of a lower optical loss. Pentafluorophenyl acrylate polymer is one of these halogen-containing acrylates.
There are two methods for preparing the pentafluorophenyl acrylate polymer, which are solution polymerization and bulk polymerization. EP 0824096 (1998) discloses a process for bulk polymerizing pentafluorophenyl acrylate monomer in an organic solvent a free radical initiator. In Example 25 of EP 0824096, 3.48 g of pentafluorophenyl acrylate (FW=252.15, 13.8 mmoles), 12.2 mg of AIBN (2,2′-azobisisobutyronitrile, FW=164.21, 0.074 mmoles) were dissolved in 17.3 ml of 2-butanone (methyl ethyl ketone) in a 50 ml three-necked flask, provided with a magnetic stirring bar, vacuum/nitrogen line, and an oil bath. After careful degassing of the reaction mixture to expell oxygen, the polymerisation was started by heating and stirring the flask's contents to about 60° C. under the exclusion of atmospheric oxygen. After 20 hours, the polymerization was discontinued, the solvent was almost completely removed by means of a rotary evaporator, the residue was redissolved in 6.5 ml of tetrahydrofurane, and the dissolved polymer was recovered through precipitation in methanol (75 ml) and filtration through a G4 glass filter. After drying in order to remove residual methanol/tetrahydrofurane (20 hours, 40° C., in vacuo), 2.3 g of poly(pentafluorophenyl)acrylate were obtained (yield about 66%) (Mw=35,800; Mn=13,415, polydispersity 2.7). The process disclosed in this European patent application not only requires the use of organic solvents in the polymerization and purification steps, but the process per se is complicated.
FR 2623510 (1989) and J. Fluorine Chem., 97, 191 (1999) both disclose bulk polymerizations of pentafluorophenyl acrylate polymer. The former uses AIBN as a initiator and dodecane thiol as a chain transfer agent, and the latter uses a photoinitiator and a thermal radical initiator to undergo a two-stage reaction. Even though these two prior art processes do not use an organic solvent, and are easier to be carried out, the polymerization products contain unreacted monomer and polymers of low polymerization degree, which deteriorate the thermal properties and quality of the polymerization products. As a result, the processing ability of the polymerization products prepared by these two prior art processes is adversely affected.